1. Field of the Invention
The present invention relates to the retrieval of data by polling a device on a network, and more particularly to a method for adjusting the polling interval according to characteristics of the network.
2. Description of the Related Art
The present invention will be described in relation to the retrieval of network management data by a network management software application. However, the skilled person will appreciate that the invention can be used for many other purposes in which data is collected by periodically polling a device on a network.
Network management applications are commonly used to monitor the performance of a network. For example, a network management application may monitor network activity to determine that the devices and links forming the network are operating efficiently, and are not unduly congested with network traffic. Monitoring typically includes “polling” network devices. Polling may involve performing tests for device activity and service availability, and sending requests to managed network devices for management data indicative of device and link operation, at predetermined periodic intervals.
For example GB-A-2 350 035 describes a network management application which performs periodic polling of devices on a Local Area Network (LAN), and which retrieves network management data using the Simple Network Management Protocol (SNMP). In accordance with the SNMP protocol, the SNMP manager in the network management station, running the network management application, sends polling requests, at periodic intervals, to the SNMP agents of managed network devices on the network to retrieve specified SNMP MIB data relating to characteristics, such as traffic activity or errors occurring at a particular port, for processing by the network management station. In addition, the network management station performs polling tests at periodic intervals, including sending ICMP Ping requests to each device on the network, and sending selected requests for services such as SMTP, NFS and DNS to servers, and monitoring the time taken to receive a response. If a response is not received in a predetermined time interval a “timeout” is recorded which may indicate that the monitored device is not operating correctly or there is a problem with a link between the monitored device and the network management station.
An example of a network management application which performs periodic polling of network devices is the 3Com® Network Supervisor, available from 3Com Corporation of Santa Clara, USA.
The polling interval for a particular request or test sent to a particular network device is typically preset in the network management application, and is dependent upon the monitored characteristic, the type of device being polled etc. Typically the polling interval is in the range of 30 seconds to 5 minutes, which, if a large number of network devices are being monitored, generates a significant quantity of network traffic that may cause congestion on the network. Moreover, if links between monitored network devices and the management station running the network management application are relatively slow speed links, the delays in the monitoring traffic may cause problems.
For example, if a network administrator is running a network management application at a location remote from the monitored network, for example via a modem connection (via the PSTN) or a Wide Area Network (WAN) link, the slow speed of the link may cause polling requests and polling responses to be delayed, thus resulting in the network management application reporting “timeouts”. Such timeouts may give the network administrator a false impression about the state of the network by suggesting that there are problems on the monitored network that do not exist.
In addition, the problem of congestion increases if a link between the network management station and the monitored network is shared with other network users, as is the case with a WAN link, since the congestion caused by the network management traffic may unacceptably slow reduce the bandwidth available to other users, thus slowing down network communications for other users.
Finally, another problem arises if the network management traffic utilised a “dial-on-demand” link, such as an ISDN line, in which the link is made upon data being sent and broken a predetermined time after the link stops being used. In particular, polling may cause the link to be continually made and broken, for example if the polling interval is 2 minutes and the line is automatically disconnected after 60 seconds of inactivity, which has undesirable cost implications and represents a poor use of the link.
In order to address these problems, the present invention provides a method for adapting the polling interval for the monitoring of a particular characteristic of a device on a network according to network characteristics, and in particular according to the nature of the links carrying the monitoring requests and responses.